1. Field of the Invention
The present invention generally relates to the cutting of glass, and more particularly, to the separation of bead portions of a glass ribbon.
2. Description of the Related Art
A common method of cutting glass is score and break separation. For this purpose, a linear defect zone is introduced mechanically into the glass, typically by using a scoring wheel. Then, the glass can be easily separated along this defect zone by applying a mechanical stress. A drawback thereof, however, is that the glass edge of a glass element obtained in this way may still exhibit defects of the previously produced defect zone. Since especially the edges are particularly critical in view of mechanical loading of the glass in the form of tensile stresses, the cutting of a glass by score and break separation may cause a considerable reduction in strength, in particular under bending stress.
Sheet glasses, in particular thin and ultra-thin glasses with thicknesses of less than 200 micrometers are nowadays commonly produced in the form of long ribbons. As a result of the production process, for example when redrawing a glass ribbon from a preform or drawing from a molten glass, thickened edge portions, so-called beads, are typically being formed along the edge of the glass ribbon. Favorably, these beads are separated once the glass ribbon has been produced, in order to facilitate the winding onto a roll in the case of thin glasses or, more generally, the further processing, among other things. Problems such as the arising of mechanical stresses caused by the thicker bead portions and entailing twisting or warping of the thin glass can be avoided in this way.
An apparatus and a method for continuous edge separation for a thin glass ribbon are known from US 2013/0126576 A1. With this apparatus, initial damage is introduced into the glass ribbon using a scoring device. The scoring device is configured as a roller including an abrasive medium, which creates defects perpendicularly to the longitudinal extension direction of the glass ribbon. While the glass ribbon is guided along its longitudinal extension direction over a curved levitation support, it is heated by a laser beam and cooled down by a fluid so as to induce thermal stresses within the glass ribbon. This causes the glass ribbon to break along its longitudinal extension direction starting from an initial defect. One drawback hereof, among others, is that the initial damage partially also extends into the quality portion of the glass ribbon, so that defects at the edge side may remain in the trimmed thin glass ribbon.
WO 2011/026074 A1 describes a method for forming a vent in a glass substrate. In this method, a laser beam is directed onto a defect and advanced over the glass surface. Additionally, a fluid jet is directed directly onto the laser spot on the glass surface such that the glass is cooled even before the temperature generated by the laser beam has been fully equilibrated across the thickness of the glass substrate. As a result, the thermal stress is limited to part of the thickness of the glass substrate, and the resulting vent only extends partially through the thickness of the glass substrate.
Both with the apparatus and method of US 2013/0126576 A1 and with the method of WO 2011/025074, the location at which the thermal stresses are produced for separating the glass is determined by the location of contact of the fluid on the glass surface. A drawback of the apparatus and the methods of the two cited documents is that this location of contact of the fluid may differ from the location on the glass surface onto which the fluid jet is directed. The reason for this is possible uncontrolled spreading of the fluid on the glass surface after the impact of the fluid jet. However, precise controlling of the location of contact of the fluid is generally advantageous for processing thin glass ribbons, in particular in order to ensure consistent edge quality and strength.
What is needed in the art is a method and apparatus for precisely controlling the contact location of the cooling fluid for processing thin glass ribbons.